A vehicle seat belt retractor includes a spindle upon which a seat belt is wound. A cinch mechanism responds to unwinding of a predetermined amount of the seat belt from the spindle by blocking further rotation of the spindle in the unwinding direction.
One such seat belt retractor including a cinch mechanism is disclosed in U.S. Pat. No. 4,726,539. The retractor disclosed in the '539 patent includes a ratchet wheel and a locking pawl. The ratchet wheel is connected to the spindle to rotate with the spindle. The locking pawl is movable into engagement with the ratchet wheel to block rotation of the ratchet wheel and the spindle in the unwinding direction.
The retractor disclosed in the '539 patent further includes a ring gear which is rotated during unwinding of the seat belt, a mode switching lever, and an overcenter spring. A pair of tabs are formed on the outside of the ring gear. Upon unwinding of a predetermined amount of the seat belt from the spindle, one of the tabs on the ring gear engages an arm on the mode switching lever to pivot the lever. The mode switching lever then causes the overcenter spring to move the locking pawl into engagement with the ratchet wheel. Upon winding of almost the entire length of the seat belt back onto the spindle, the other tab on the ring gear engages another arm on the mode switching lever. The mode switching lever again pivots and causes the overcenter spring to move the locking pawl back out of engagement with the ratchet wheel.